Real-time measurement or estimation of road surface condition are important and useful to vehicle control systems such as adaptive cruise control (ACC), anti-lock braking systems (ABS), electronic stability program (ESP) and acceleration slip regulation (ASR). Reliable and accurate road surface condition information is important for such systems to function as intended. Typical road surface evaluation systems attempt to estimate road friction coefficients through estimation schemes that require certain levels of vehicle longitudinal and/or lateral motion excitations (e.g. accelerating, decelerating and steering) and a persistence of such excitation levels in order to achieve a reliable friction estimation. While such schemes are valid in theory, attaining the requisite level and persistence of excitation to achieve a reliable friction estimation, however, has proven problematic in practice.
Accordingly, an improved reliable and robust system and method for estimating road surface friction is desired for use in advanced vehicle control systems.